Wet master batches have been produced for the purpose of improving a rubber composition containing a filler such as a carbon black in terms of workability and dispersibility of the filler in the rubber composition. The wet master batches are generally produced through a method including: a given rubber latex solution preparation step of compounding and preparing a rubber latex solution by optionally adding a surfactant and water to a latex of natural rubber or synthetic rubber; a filler slurry preparation step of compounding and preparing a slurry solution containing a filler such as a carbon black dispersed in a solvent such as water; a mixing and coagulating step of continuously mixing and coagulating the rubber latex solution and the filler slurry prepared in the steps above so as to form a coagulation solution containing a coagulum; a solid-liquid separating step of separating and taking out only the coagulum from the coagulation solution thus formed; a cleaning step of cleaning the coagulum thus separated, so as to remove impurities such as solidifier attached or contained in the coagulum; a dehydrating step of removing water filled in the inner gaps of the cleaned coagulum; a drying step of drying the coagulum thus dehydrated; and an optional molding step of molding the dried coagulum into a desired shape such as in the form of granules or in the form of a sheet, to thereby form a wet master batch as a product.